Declaring hxt_omp.h as extern "C" in C++ files leads to compile errors with g++ version 15.1.0

When I try to compile Gmsh in MSys2 with the gcc-compilers version 15.1.0, I get errors about "template with C linkage" in omp.h. It turns out that the compiler's omp.h checks if it is used by a C++ compiler. If so, it defines some templates.

The header hxt_omp.h, which includes omp.h, seems to be used in C and C++ files. The two C++ source files contrib/hxt/tetBR/src/hxt_boundary_recovery.cxx and src/mesh/meshGRegionHxt.cpp include hxt_omp.h within an extern "C" {} section, which cause the problems. Moving out #include "hxt_omp.h" from the extern "C" {} section and apply it upfront solves the issue and Gmsh compiles fine.

diff --git a/contrib/hxt/tetBR/src/hxt_boundary_recovery.cxx b/contrib/hxt/tetBR/src/hxt_boundary_recovery.cxx
index a616c3f8f..95b0d9379 100644
--- a/contrib/hxt/tetBR/src/hxt_boundary_recovery.cxx
+++ b/contrib/hxt/tetBR/src/hxt_boundary_recovery.cxx
@@ -1,7 +1,7 @@
+#include "hxt_omp.h"
 extern "C" {
 #include "hxt_mesh.h"
 #include "hxt_tools.h"
-#include "hxt_omp.h"
 #include "predicates.h"
 }

diff --git a/src/mesh/meshGRegionHxt.cpp b/src/mesh/meshGRegionHxt.cpp
index 75ea026bd..98c8a5464 100644
--- a/src/mesh/meshGRegionHxt.cpp
+++ b/src/mesh/meshGRegionHxt.cpp
@@ -24,8 +24,8 @@

 #if defined(HAVE_HXT)

-extern "C" {
 #include "hxt_omp.h"
+extern "C" {
 #include "hxt_tetMesh.h"
 #include "hxt_tetDelaunay.h"
 }